JP2000208135A - Nonaqueous electrolyte positive electrode and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniform the charging depth of an active material in each part within a positive electrode plate by constituting the positive electrode plate into a porous structure having a lithium transition metal composite oxide reversibly storing and releasing lithium ion and a mix containing a conductive agent and a binder, and providing a layer consisting of a carbon material in the pores. SOLUTION: A lithium cobalt composite oxide is used as positive electrode active material, and the lithium cobalt composite oxide is retained by aluminum foil as current collector to form a positive electrode plate. Namely, the positive electrode plate having a porous structure is produced by mixing polyvinylidene fluoride as binder, acetylene black as conductive agent, and the lithium cobalt composite oxide as active material, properly adding N-methyl pyrolidone to prepare a paste, and applying the paste to both sides of the aluminum foil as current collector followed by drying. The positive electrode plate is thereafter dipped in a paste consisting of acetylene black as carbon material followed by drying to form the layer of acetylene black in the pores.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a positive electrode for a non-aqueous electrolyte battery and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, electronic devices such as a portable radio telephone, a portable personal computer, and a portable video camera have been developed, and various electronic devices have been reduced in size to be portable. Along with this, a battery having a high energy density and a light weight is also adopted as a built-in battery. A typical battery that satisfies such a requirement is an active material such as lithium metal or lithium alloy, or a host material containing lithium ions (here, a host material refers to a material that can occlude and release lithium ions). Lithium intercalation compound occluded in a certain carbon is used as a negative electrode material, and LiC
This is a non-aqueous electrolyte secondary battery using an aprotic organic solvent in which a lithium salt such as 10 ₄ or LiPF ₆ is dissolved as an electrolyte.

This non-aqueous electrolyte secondary battery has a negative electrode plate in which the above-mentioned negative electrode material is held on a negative electrode current collector as a support, and a reversible electrochemical reaction with lithium ions such as a lithium-cobalt composite oxide. The positive electrode plate, which holds the positive electrode active material that reacts on the positive electrode current collector that is the support, from the separator that holds the electrolytic solution and intervenes between the negative electrode plate and the positive electrode plate to prevent a short circuit between the two electrodes Has become.

The above-mentioned positive electrode plate, separator and negative electrode plate are each formed of a thin sheet or foil and laminated or spirally wound in order to form a battery container made of a metal laminated resin film having an airtight structure. Is stored in.

When this non-aqueous electrolyte secondary battery is used in electronic equipment, a predetermined voltage is obtained as a unit cell or a plurality of cells connected in series. The single or plural batteries are housed in a housing made of resin or metal and resin together with the charge / discharge control circuit, and sealed so that the contents cannot be taken out, and used as a battery pack.

[0006]

A secondary battery capable of being repeatedly charged and discharged has a high energy density, a high discharge capacity, a high discharge performance such as a high load discharge, a low temperature discharge, and a high charge such as a rapid charge and a low temperature charge. It is desirable to have charging performance. In a non-aqueous electrolyte battery, if the charging performance is poor, metallic lithium will precipitate in a dendritic manner on the surface of the negative electrode plate during rapid charging with a large current. When the metal lithium on the tree grows, it reaches the positive electrode plate and causes an internal short circuit, which generates heat, ruptures, and the like of the battery, and damages equipment and users to which the battery is mounted. It is considered that as one means for solving this problem, there is an effect of improving the charge acceptability of the negative electrode and the charge acceptability of the positive electrode.

Here, the inventor of the present application has found that after rapidly charging a rectangular nonaqueous electrolyte battery in which the current collecting lead of the positive electrode plate is at the center of winding of the element and the negative electrode lead is at the outermost periphery of the element, in a dry environment, Disassembling the non-aqueous electrolyte battery that had been rapidly charged and observing the electrodes revealed that the amount of deposited metallic lithium per unit area on the surface of the negative electrode plate facing the current collecting lead of the positive electrode plate was the largest. Was.

Further, the battery is disassembled as described above, and the positive electrode plate is taken out. From the portion near the current collecting lead, near the center, and the portion farthest from the current collecting lead, 2
A positive electrode plate was cut out at a size of × 2 cm, and EC / DEC = 1: 1, 1M LiClO _{4 using} lithium metal as a reference electrode.
When the electrode potential was measured in the electrolytic solution, it was found that the potential of the positive electrode plate closest to the current collecting lead of the positive electrode plate was the highest.

From these results, it is presumed that one of the causes of the deposition of metallic lithium on the surface of the negative electrode plate during rapid charging is that the depth of charge of the positive electrode active material in each part of the positive electrode plate is not uniform. That is, in the positive electrode plate, since the depth of charge of the positive electrode active material near the positive electrode current collecting lead having the shortest conductive path is deep, the depth of charge of the negative electrode opposed to that portion also becomes high, causing precipitation of metallic lithium. It is presumed that.

[0010] Due to the non-uniform charge depth of the active material in the thickness direction of the positive electrode plate, deposition of metallic lithium on the negative electrode plate facing the portion may be considered. In the thickness direction of the positive electrode plate, the positive electrode active material that is close to the current collector is considered to have a substantially uniform charge depth, but as the distance from the current collector increases, the conductive path from the current collector increases. It is considered that only a good active material has a high charge depth. In the active material near the surface of the positive electrode plate located at the longest distance from the current collector, it is considered that the unevenness of the charging depth becomes remarkable. That is, in the positive electrode active material near the surface of the positive electrode plate, the better the conductive path from the current collector, the higher the depth of charge, and the negative electrode facing this part also has a higher depth of charge, which causes precipitation of metallic lithium. it is conceivable that.

Therefore, in order to suppress the deposition of metallic lithium on the surface of the negative electrode during rapid charging, it is necessary to make the depth of charge of the positive electrode active material in each part in the positive electrode plate uniform.

Here, in order to make the charge depth of the active material in each part in the positive electrode plate uniform, increasing the amount of the conductive material in the positive electrode mixture is one of the means. However, the conductive agent mixed in the mixture paste during the positive electrode plate manufacturing process has a property of agglomeration, and a large amount of the conductive agent is required to secure conductivity within the positive electrode plate. Is undesirable because it leads to a decrease in the energy density of the electrode and the battery.

[0013]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in view of the problem that the depth of charge of the positive electrode active material is nonuniform in each part in the positive electrode plate.

The present invention provides a positive electrode plate for a non-aqueous electrolyte battery having a porous structure comprising a mixture containing a lithium transition metal composite oxide that reversibly stores and releases lithium ions, a conductive agent and a binder. It is characterized in that a layer made of a carbon material is provided in the pores existing therein.

Further, according to the present invention, a mixture obtained by adding an organic solvent to a mixture containing a lithium-transition metal composite oxide, a conductive agent and a binder is applied to a current collector, and a dried electrode plate is made of a carbonaceous material. A method for producing a positive electrode for a non-aqueous electrolyte battery having a layer made of a carbon material in pores present in an electrode, characterized by immersing and drying in a mixture containing a thickener, a binder and a dispersant. It is due to.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described based on embodiments with reference to the drawings.

Embodiment 1 FIG. 2 is a view showing the appearance of a non-aqueous electrolyte secondary battery according to the present invention. In FIG. 2, 1
Is a non-aqueous electrolyte secondary battery, 2 is a metal laminated resin film case, 3 and 4 are heat welded portions of the metal laminated resin film case, 5 is a positive terminal, and 6 is a negative terminal. A laminated film case 2 in which an electrode group consisting of a positive electrode plate, a separator and a negative electrode plate is heat-welded to a metal laminated resin film together with a non-aqueous electrolyte (not shown).
Stored in.

As the positive electrode active material, a lithium-cobalt composite oxide was used. The positive electrode plate is obtained by holding the above-mentioned lithium cobalt composite oxide on an aluminum foil having a thickness of 10 μm as a current collector. A positive electrode plate having a porous structure is prepared by mixing 6 parts of polyvinylidene fluoride as a binder, 3 parts of acetylene black as a conductive agent, and 91 parts of lithium-cobalt composite oxide as an active material, and appropriately mixing N-methylpyrrolidone. Was prepared in the form of a paste, and then applied to both sides of an aluminum foil as a current collector and dried.

Next, 30 parts of acetylene black as a carbon material, 10 parts of polyvinylidene fluoride as a thickener and a binder, and N-methylpyrrolidone 6 as a dispersion medium
0 parts were mixed to prepare a paste, and the positive electrode plate was immersed in the paste and dried to form an acetylene black layer in the holes of the positive electrode plate.

The negative electrode plate is prepared by mixing 92 parts of graphite (graphite) as a host substance and 8 parts of polyvinylidene fluoride as a binder on both sides of a current collector, and adding N-methylpyrrolidone as appropriate to form a paste. Was prepared by coating and drying both surfaces of a 14 μm-thick copper foil as a current collector.

The separator was a microporous polyethylene membrane, and the electrolyte was a mixed solution of ethylene carbonate: diethyl carbonate = 4: 6 (volume ratio) containing 1 mol / l of LiPF ₆ .

The dimensions of the electrode plate are as follows.
Width 49mm, separator thickness 25μm, width 53mm,
The negative electrode plate has a thickness of 170 μm and a width of 51 mm, and is superposed in order, centering on a rectangular core of polyethylene,
After being wound in an elliptical shape around it, it was stored in a metal laminated resin film case.

FIG. 3 shows a cross section taken along line AA 'of the nonaqueous electrolyte secondary battery shown in FIG. In FIG. 3, 1
0 is a 12 μm thick PET film for protecting the surface of the outermost layer, 11 is a 9 μm thick aluminum foil as a barrier layer, and 12 is an acid-modified polyethylene layer having a thickness of 100 μm as a heat welding layer. The laminated film case of No. 10 was composed of 10, 11 and 12, and the outermost PET film 10 for surface protection and the aluminum foil 11 as a barrier layer were bonded with a urethane-based adhesive.

In FIG. 3, a positive electrode lead terminal 5 and a negative electrode lead terminal 6 are formed on a 50 to 100 μm thick metal conductor such as copper, aluminum, nickel or the like by forming a 50 μm thick acid to form an adhesive layer with a metal. A modified PE layer is adhered, and an evar resin (ethylene-vinyl alcohol copolymer resin manufactured by Kuraray) layer having a thickness of 70 μm as an electrolyte barrier layer is provided outside the modified PE layer. When these were overlapped and bonded as shown in FIG. 3, good airtightness was obtained. In this way, a non-aqueous electrolyte battery having a design capacity of 520 mAh
Made individually.

Example 2 In Example 1, the composition of the paste for forming the carbon material layer on the positive electrode plate was 40 parts of acetylene black, 20 parts of polyvinylidene fluoride,
Fifty non-aqueous electrolyte batteries having the same design capacity of 520 mAh as in Example 1 were produced except that N-methylpyrrolidone was 40 parts.

Example 3 The composition of a paste for providing a carbon material layer on a positive electrode plate was as follows: 30 parts of graphite, 10 parts of polyvinylidene fluoride, and 60 parts of N-methylpyrrolidone.
520 mAh, the same design capacity as in Example 1 except that
50 non-aqueous electrolyte batteries were manufactured.

Example 4 The composition of the paste for providing the carbon material layer on the positive electrode plate was as follows: 30 parts of hard carbon, 10 parts of polyvinylidene fluoride, and N-methylpyrrolidone 6
The same design capacity as that of Example 1 except that it was set to 0 parts, 520 mA
h, 50 non-aqueous electrolyte batteries were manufactured.

[Comparative Example] Fifty batteries having the same design capacity of 520 mAh as in Example 1 were produced, except that a conventional one in which no carbon material layer was provided on the positive electrode plate was used.

The batteries of Examples 1, 2, 3, 4 and the comparative example were each 10 cells at 1200 mA (about 2.
(3 CmA equivalent; 1 CmA = 520 mA) at a current of 4.1
After charging for 3 hours to V, the battery was disassembled in a dry atmosphere, and the properties of the electrodes and separator were visually observed. As a result, silver-grey metallic lithium was precipitated all over the surface of the negative electrode plate of the battery of the comparative example corresponding to the conventional product, and the metallic lithium was adhered to the surface of the separator in contact with the negative electrode plate. In particular, the deposition of metallic lithium was remarkable on the negative electrode surface facing the active material near the current collecting lead of the positive electrode plate.
On the other hand, no metallic lithium was deposited on the negative electrode plate surfaces of the batteries of Examples 1, 2, 3, and 4.

Further, in the positive electrode plate taken out after disassembly of the battery, a portion closest to the current collecting lead, near the center of the positive electrode plate,
A portion having the longest distance from the current collecting lead was cut out to a size of 2 × 2 cm, and EC / D was determined using metallic lithium as a reference electrode.
The electrode potential was measured in an EC = 1: 1, 1M LiClO ₄ electrolyte. In the case of the comparative example, the potential of the portion of the positive electrode plate closest to the current collecting lead was the highest, and the potential decreased as the distance from the current collecting lead became longer. On the other hand, in the case of the example of the present invention, the potential was almost the same irrespective of the location of the positive electrode plate from which the sample was cut out.

Further, 1 CmA (= 520 mA) /4.1
FIG. 1 shows a charging curve when the battery was charged at V for 3 hours. In FIG. 1, A shows the charging curve of the batteries of Examples 1, 2, 3, and 4, and B shows the charging curve of the comparative example. As shown in FIG. 1, the batteries of Examples 1, 2, 3, and 4 of the present invention had smaller polarization during charging than the batteries of Comparative Examples. That is, the polarization of the positive electrode plate can be reduced by providing the carbon material layer on the positive electrode plate.

Next, 40 cells of each of the batteries of Examples 1, 2, 3, 4 and the comparative example were charged at a charging current of 1 CmA, 2 CmA, 3 CmA, 5 CmA to 4.1 V at room temperature.
Table 1 shows the average discharge capacity when the battery was charged to 2.75 V at 1 CmA after charging for 3 hours.

[0033]

[0034]

[Table 1]

According to Table 1, Examples 1, 2, and 3 according to the present invention are shown.
It can be seen that the batteries Nos. 4 and 4 have excellent quick charge performance. This is because when the battery of the comparative example was rapidly charged, metallic lithium was deposited on the surface of the negative electrode plate, and most of the metallic lithium did not participate in the discharge reaction. Thus, Embodiments 1 and 2 according to the present invention
In the batteries of Nos. 3 and 4, since the carbon material layer was provided in the pores of the positive electrode plate, the deposition of metallic lithium deposited on the negative electrode surface was suppressed, so that the decrease in the discharge capacity was small even during high-rate charging. It is considered something.

The power generating element used in the present invention is not limited to the shape in which the positive electrode plate, the separator, and the negative electrode plate are wound as described in the embodiment, and a flat electrode plate formed in a foil shape is laminated. Shaped shapes and the like can also be used.

Further, in the above-described embodiment, the lithium-cobalt composite oxide is used as the compound capable of inserting and extracting lithium as the positive electrode material. However, the present invention is not limited to this. Some or all of the lattice positions occupied by atoms are nickel,
It may be substituted with one or more transition metal atoms such as manganese and aluminum.

Further, in the above embodiment, graphite is used as the compound as the negative electrode material. In addition, alloys of lithium with Al, Si, Pb, Sn, Zn, Cd, etc., LiFe ₂ O ₃ , WO _2, MoO transition metal oxides such as _2, graphite, carbonaceous materials such as carbon, L
Lithium nitride such as i ₅ (Li ₃ N), or lithium metal foil, or a mixture thereof may be used.

Further, as a solvent for the electrolytic solution, a mixed solution of ethylene carbonate and diethyl carbonate is used in the embodiment. However, the present invention is not limited to this. Ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, γ- Butyrolactone, sulfolane, dimethylsulfoxide, acetonitrile, dimethylformamide, dimethylacetamide,
A polar solvent such as 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolan, methyl acetate, or a mixture thereof may be used.

Further, in the examples, the insulator used was an insulating polyethylene microporous membrane, which was impregnated with an electrolytic solution. However, other than this, a polymer solid electrolyte, a polymer solid electrolyte was used. A gel electrolyte containing an electrolyte solution can also be used. Further, an insulating microporous film and a solid polymer electrolyte may be used in combination. Further, when a porous solid polymer electrolyte membrane is used as the solid polymer electrolyte, the electrolyte contained in the polymer and the electrolyte contained in the pores may be different.

Further, in the examples, the paste used for forming the high conductor layer in the holes of the positive electrode plate was a conductive agent, a thickener, polyvinylidene fluoride as a binder, and N as a dispersion medium. Although a mixture of -methylpyrrolidone was used, the thickness of the carbon material layer provided in the pores of the positive electrode plate can be adjusted by changing these ratios.
The composition of the paste for providing the carbon material layer may be appropriately changed according to the amount and diameter of the holes in the manufactured positive electrode plate.

In the examples, acetylene black was used as the carbon material. However, the present invention is not limited to this, and carbon materials having high conductivity such as graphite, hard carbon, soft carbon, and composite materials thereof are used. Any may be used.

Further, polyvinylidene fluoride was used as the thickener and the binder, but the present invention is not limited to this. For example, rubber materials such as styrene-butadiene rubber, and binders such as polytetrafluoroethylene, polyethylene, and polypropylene are used. Highly polymer materials can be used.

[0044]

The positive electrode plate according to the present invention has a porous structure,
A carbon material layer is provided in the pores of the positive electrode. Since the carbon material layer is a highly conductive material, the electric conductivity in the thickness direction of the positive electrode plate is uniform in all parts of the positive electrode plate. As a result, even during rapid charging, the depth of charge of the active material in all parts of the positive electrode plate becomes uniform, suppressing the deposition of metallic lithium on the surface of the negative electrode plate facing the positive electrode plate, thereby reducing the time of rapid charging of the battery. Safety can be ensured. The nonaqueous electrolyte battery using the positive electrode plate according to the present invention is extremely useful as a power source for portable electronic devices.

[0045]

[Brief description of the drawings]

FIG. 1 is a charging curve at the time of rapid charging in Examples and Comparative Examples according to the present invention.

FIG. 2 is a diagram showing the appearance of a non-aqueous electrolyte secondary battery according to the present invention.

FIG. 3 is a sectional view taken along line AA ′ of the nonaqueous electrolyte secondary battery according to the present invention.

Claims (2)

[Claims] 1. A porous structure comprising a lithium transition metal composite oxide that reversibly stores and releases lithium ions, a mixture containing a conductive agent and a binder, and a layer made of a carbon material is provided in the pores. A positive electrode for a non-aqueous electrolyte battery, characterized in that: 2. A current collector obtained by applying a mixture obtained by adding an organic solvent to a mixture containing a lithium transition metal composite oxide, a conductive agent and a binder to a current collector, and drying the electrode plate with a carbonaceous material, a thickener and The method for producing a positive electrode for a non-aqueous electrolyte battery according to claim 1, wherein the positive electrode is immersed and dried in a mixture containing a binder and a dispersant.